Industrial lasers are used for a variety of machining operations. One such operation includes using a laser to create holes completely or partially through a workpiece. In the case of a workpiece in the form of a thin-walled shell, it is often desirable to use a laser to form a hole extending through a wall of the workpiece. Due to the geometry of some workpieces, a situation may arise wherein, after the desired hole is formed in a first surface of a workpiece, the laser beam used to drill the hole impinges on a second surface of the workpiece. As shown in FIG. 1, for example, a laser beam 2 is used to form a hole in a first surface 4 of a workpiece 6. After laser beam 2 penetrates first surface 4, laser beam 2 impinges on a second surface 8. Impinging on second surface 8 in this manner can undesirably affect second surface 8. Specifically, second surface 8 can be unintentionally and undesirably machined or heat treated. For example, a laser beam being used to drill orifices in a fuel injector nozzle can impinge on and undesirably affect interior surfaces of the fuel injector nozzle.
One way to prevent a laser beam from impinging on a surface of a workpiece is to block the laser beam with a mask. An example of this strategy is described in U.S. Pat. No. 6,070,813 (the '813 patent) issued to Durheim on Jun. 6, 2000. The '813 patent describes interposing a backing material between a first interior surface and a second untargeted interior surface to prevent a laser beam from passing through the first interior surface and impinging on the second untargeted interior surface. The backing material is a block of one of the following groups of materials: tungsten, tungsten carbide, ceramic, or other high temperature material. These materials have the ability to absorb a large amount of laser energy without disintegrating. The backing material is separated from the first interior surface by an air gap, which allows the laser beam to diverge, thereby reducing the power density of the beam that strikes the backing material. In addition, the gap allows convective air currents to cool the backing material. The backing material is replaced if formation of a passageway in the first interior surface damages the backing material such that it is unable to block the laser beam and protect the second untargeted interior surface.
Other types of prior art masks have a cylindrical shape and are made from glass fibers that scatter and absorb energy of laser beams. The glass fibers are typically cylindrical with substantially flat ends.
Although the backing material of the '813 patent and other types of prior art masks may initially protect untargeted interior surfaces from laser beams used to create holes, they may fail during long and/or repetitive machining operations. Specifically, bonds between molecules and/or atoms of the materials used in the block of the '813 patent and/or in other prior art masks (glass) are unable to withstand long and/or repetitive machining operations. Additionally, laser beams can leak through the gap of the '813 patent around the backing material of the '813 patent. Similarly, laser beams can leak around cylindrically shaped glass fibers. Leaked laser beams can impinge on untargeted surfaces, causing undesired heating and machining of these untargeted surfaces.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems in the art.